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Fall
Plow vs Disk-Ripper after Winter Wheat for Spring Barley
Kevin
Scholz
with Roger Veseth, Baird Miller, Stewart Wuest, and John Burns,
WSU Coop. Ext.
Lavaine Logan, St. John Hardware, Fairfield; and Dennis Roe, USDA-NRCS,
Colfax
Objective
Test the concept
that reducing tillage intensity on more erodible, water-short portions
of field landscapes could improve soil erosion protection, precipitation
storage efficiency and crop yield potential.
Location: Colfax,
WA Landscape position: 25-30% slope with SSE exposure
Annual precipitation: 17 inches Previous crop: 85 bu/A winter wheat
Soil: Palouse silt loam Rotation: Winter wheat, spring barley, fallow
Treatments
(in undisturbed winter
wheat stubble)
- Moldboard plow
without trashboards to a depth of 7 inches and furrow turned uphill
on October 10, 1993
- Disk-subsoil with
a Sunflower disk-ripper with 20-inch front tandem disk at 3-inch depth
and 7-shank straight-point rippers on 2-ft spacings at 12-inch depth
on October 22, 1993
Comments
Plots were arranged
end-to-end along the contour in the top 80 feet of a divided-slope field
division. Plot lengths ranged from 300 to 450 feet. Plow treatments were
established first, with the plow being pulled out to cross disk-ripper
plots. The disk-ripper plots were established later with a zigzag pattern,
turning on the adjourning plowed plot. These turning margins were excluded
from data collection.
The disk-ripper resulted
in similar tillage impacts on residue and roughness as with disking after
harvest and late-fall chiseling, a common sequence of operations in this
production region. However, residue occasionally bunched up on the ripper
shanks and caused some plugging problems and subsequently reduced stand
establishment in those areas. Chisel shank plugging usually does not occur
with the separate disk and chisel operations because the fall chiseling
is delayed until after rains and a harrowing operation to help pack the
residue and soil. With this combined disk-ripper operation, the residue
was "fluffy" and dry, causing more plugging problems. Areas
with equipment plugging problems were avoided in the stand counts and
residue measurements.
Spring pre-tillage
residue samples were taken on March 4 with 9.6 square ft. cable hoops.
Two subsamples were taken in each plot. Six-foot deep soil samples were
taken at foot increments on March 9, 1994. Three subsamples were taken
per plot. The 6-foot samples were analyzed for nitrate nitrogen, ammonium
nitrogen in the top three feet, plant-available soil water, and other
standard nutrient/soil property tests.
Spring field operations
on all plots included: harrowing, field cultivation, shank fertilizer
application (65 lb N/A on 12-inch spacing), rod weeding, and seeding to
Steptoe spring barley on March 15 with a conventional International double-disk
drill with 7-inch row spacings. Starter fertilizer of 16-20-0-0 was applied
at a rate of 50 lb/A. Both the field cultivator and fertilizer injector
pulled some buried residue back to the surface (observational, not measured).
The surface residue was dry and brittle at seeding time, allowing the
disks to cut through the residue with little straw tucking in the seed
furrow. A 0.3-inch rain fell shortly after seeding. Stand counts were
taken on May 3.
Preharvest samples
of two rows one meter long were clipped near ground level one week before
harvest. Measurements included number of heads, total biomass weight,
grain weight, and 1000 kernel weight.
Data
Yield,
lb/A, harvested 8 Aug 94.
|
Treatment |
Rep 1 |
Rep 2 |
Rep 3 |
Rep 4 |
Average |
|
Plow |
2090 |
2609 |
(2603) |
2448 |
2437.5a |
|
Disk-ripper |
2565 |
2887 |
(1902 |
2820 |
2757.3b |
|
LSD (5%) |
|
|
|
|
245 |
|
CV |
|
|
|
|
2.7% |
Spring
pre-tillage surface residue level (lb/A)
|
Treatment |
Rep 1 |
Rep 2 |
Rep 3 |
Rep 4 |
Average |
|
Plow |
1015 |
998 |
1487 |
1247 |
1186.8a |
|
Disk-ripper |
3278 |
4182 |
2706 |
3138 |
3326.0b |
|
LSD (5%) |
|
|
|
|
1304 |
|
CV |
|
|
|
|
26% |
Plant-available
soil water (inches) in the top 3 feet, March 9, 1994.
|
Treatment |
Rep 1 |
Rep 2 |
Rep 3 |
Rep 4 |
Average |
|
Plow |
5.13 |
5.58 |
5.21 |
5.51 |
5.36a |
|
Disk-ripper |
6.30 |
6.16 |
5.73 |
5.94 |
6.03b |
|
LSD (5%) |
|
|
|
|
0.53 |
|
CV |
|
|
|
|
4.2% |
Percent
surface residue after seeding, (four 50-ft line-point transects
per plot on April 19
|
Treatment |
Rep 1 |
Rep 2 |
Rep 3 |
Rep 4 |
Average |
|
Plow |
35 |
46 |
50 |
46 |
44.3a |
|
Disk-ripper |
59 |
76 |
67 |
67 |
67.3b |
|
LSD (5%) |
|
|
|
|
8.71 |
|
CV |
|
|
|
|
7.0% |
Conclusion
The spring surface
residue level in the disk-ripper plots was 2.8 times that following plowing
(3326 vs 1187 lb/A). Percent surface residue after seeding spring barley
was also significantly higher (67 vs 44%). It should be noted that the
level of surface residue following the uphill plowing is substantially
higher than is typically present after plowing if the plow furrow is turned
down slope. The higher level of surface residue under the disk-ripper
significantly increased overwinter soil water storage (.64 inches) in
the top 3 feet of soil. There was no evidence of water loss from surface
runoff overwinter or during barley establishment, so the difference in
soil water availability overwinter is due largely to evaporation. There
were no significant differences in nitrate nitrogen, ammonium nitrogen,
or total-plant-available soil water in the 6-foot profile. The increased
overwinter soil water storage, plus the possibility of continued lower
soil water evaporation (not measured) prior to barley canopy cover, probably
allowed the significant yield increase (320 lb/A) with the disk-ripper.
Data from the small
pre-harvest samples indicated a higher trend in yield, residue production,
and number of kernels per head with the disk-ripper compared to the plow,
although differences were not statistically significant due to high variability
between replications.
Surface residue levels
will be determined on each plot through the 1995 winter wheat planting
on summer fallow to evaluate the effect of these 1993 primary tillage
operations on subsequent water erosion potential.
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